GB2377438A

GB2377438A - Producing glass balls

Info

Publication number: GB2377438A
Application number: GB0216089A
Authority: GB
Inventors: Hatto Schaefer; Christian Schenk; Horst Wolf; Andreas Walsdorf
Original assignee: Carl Zeiss AG
Current assignee: Carl Zeiss AG
Priority date: 2001-07-13
Filing date: 2002-07-11
Publication date: 2003-01-15
Anticipated expiration: 2022-07-11
Also published as: JP2003048731A; JP4138383B2; CN1397508A; DE10134198A1; GB0216089D0; US20030051506A1; FR2827273B1; GB2377438B; CN1277770C; FR2827273A1; DE10134198B4

Abstract

A method of producing glass balls, comprises feeding a glass flow (11) between two rollers, (20.1,20.2) which are driven synchronously but contrarotatingly in the flow direction, from a feed tank (10) containing a mass of molten glass, said rollers having hemispherical depressions (21) distributed over the circumference and forming spherical beads (12) on a thin glass strip (13) successively in the region of an imaginary contact tangent, (the thickness of the glass strip being fixed by the spacing between the rollers externally of the depressions in the region of the contact tangent), separating the crude balls (14) from the glass strip by means of a separating device (15) once the glass strip (13), containing the spherical beads, has been cooled, and subjecting these crude balls (14) to a cold surface finishing treatment.

Description

METHOD AND APPARATUS FOR PRODUCING GLASS BALLS

The invention relates to a method and an apparatus for producing glass balls.

Known methods are very complex and, in consequence, incur high production costs. It is thus known to cut manageable pieces or pellets from a glass block and then to round them and rough-grind them in a drum. The crude balls thus produced are ground coarsely, ground finely, lapped and polished, i.e. they are subjected to a plurality of cold finishing treatments. The same disadvantages also exist when cylindrical portions are separated from glass rods as initial components. When producing the glass rods, constrictions are made which are shaped to form balls. The strand of glass may also be severed by air pressure or by means of a rotating disc, so that small glass particles are sprayed or centrifuged, said particles being shaped to form balls by surface tension. In such case, however, the size of the balls being produced is already limited to a diameter range less than 1 mm.

An object of the invention is to provide a method of producing glass balls, whereby a plurality of crude balls, even those of a relatively large diameter, can be produced very easily.

This method is characterized, according to the invention, in that a glass flow is fed between two rollers, which are driven synchronously but contrarotatingly in the flow direction, from a feed tank containing a mass of molten glass, said rollers having hemispherically shaped depressions distributed over the circumference and forming spherical beads on a thin glass strip successively in the region of an imaginary contact tangent, in that the thickness of the glass strip

I by the spacing between the rollers externally of the depressions in the of the contact tangent, in that crude balls are separated from the glass y means of a separating device once the glass strip, containing the al beads, has been cooled, and in that these crude balls are subjected to surface finishing treatment.

n glass strip, containing the spherical beads, comprises a plurality of ails which, after being cooled, can easily be separated from the thin glass means of a separating device, since the thin glass strip is in the form of tided breaking location. In such case, the separation may be effected in a case, it is important that the two rollers are driven synchronously and Takingly, and that the depressions are so disposed on the roller casing y are constantly aligned with one another in the region of the imaginary tangent and form the spherical beads. It is necessary to prevent the irons, which encounter one another, from becoming offset from one on the circumferential side or axially, and this can be achieved in the t way by driving the rollers in a correspondingly synchronously regulated Since the crude balls are obtained at relatively low cost, additional ns prior to the cold finishing treatment are no longer necessary.

the crude balls can easily be separated from the glass strip, one nent makes provision for the glass strip, between the spherical beads, to form of intended breaking locations having a thickness of about 1.5 mm.

thicknesses no longer represent good intended breaking locations. In ! of smaller thicknesses, there is the danger that, during the separating cracks may also be formed in the region of the crude balls.

According to an additional embodiment, provision is made for the rollers to be heated-up to about 270 to 300 C by means of radiation heat.

This method avoids differences in temperature which are too great between the rollers and the glass strip containing the beads, and cracks are prevented from forming in the glass.

In the case where types of glass have low viscosity (short ?7 development curve), one pair of rollers is generally sufficient for the drawing system, since the solidifying process and a sufficiently thin rolling-out process are concluded at roughly the same time. In the case of more viscous glass types (longer ?; development curve), these two mechanisms are not achieved with one pair of rollers. A cascade of rollers, having 2 to 3 pairs of rollers, is to be provided.

So that the glass flow travels uniformly along the rollers and enters the depressions, a further development makes provision for the glass flow to be supplied to the rollers from the feed tank with a temperature of between 1000 and 1200 C and a low viscosity of between 1 and 50 dPas, preferably about 10 dPas, at a throughflow rate of between 200 and 250 g/min. In the case of glasses which are too viscous, the glass strip, that is to say the intended breaking locations, cannot be rolled thinly enough.

So that the beads already assume as good a spherical configuration as possible, the diameter of the rollers can be selected to be between 100 and 250 mm, and the radius of the depressions can be selected to be between 3 and 10 mm.

In order to utilise in optimum manner the roller circumference for the formation of beads, one embodiment makes provision for rollers to be used, wherein the depressions are disposed in circumferential rows on the roller surfaces with

spacings therebetween, the adjacent circumferential rows being lived with each other so as to be offset from each other by half a spacing.

sequence, the glass strip, as the intended breaking location and carrier of clerical beads, is limited to short lengths between the beads.

aratus for producing glass balls according to the method of the invention cterised in that a glass flow can be supplied from a feed tank, containing of molten glass, to a shaping device having two rollers, which are driven Venously and contrarotatingly and have hemispherical depressions to form lass strip having spherical beads, in that, once the glass strip has cooled, ads are separable from the glass strip as crude balls by means of a :ing device, and in that the crude balls are then subjected to a cold surface treatment, the final cold finishing treatment being accomplishable in manner to the desired extent.

Stood and the apparatus according to the invention are explained more h reference to one schematic drawing.

d tank 10 of an apparatus may be, for example, the drawing container for fig system of a plate glass system, in which tank the mass of molten glass fed to the two contrarotatingly driven rollers 20.1 and 20.2 as glass flow n outlet slot.

faces of the rollers 20.1 and 20.2 are provided with circumferential rows spherical depressions 21, which are disposed at uniform spacings from ther and are each separated from the other by circumferential regions 22 fillers 20.1 and 20.2. A gap, which determines the thickness of the glass flowing therethrough, therefore remains at the location with the smallest between the rollers 20.1 and 20.2, which rotate in the flow direction of

the glass flow 11, i.e. at the ideal contact tangent, while the depressions 21 of the two rollers 20.1 and 20.1, which encounter one another when aligned in this region, form spherical beads 12 in this glass strip 13. In such case, the depressions 21, which extend into the narrowest zone, are initially filled with the glass flow 11, which is compressed to form the beads 12 as it passes the location with the gap. The gap is selected to be between 1.3 and 1.5 mm, and the glass flow 11 is conveyed through the rollers 20.1 and 20.2 with a temperature of between 1000 and 1200 C at a throughflow rate of 200 to 250 g/min. In such case, a mass of molten glass is used, which has a low viscosity of between 1 and 50 dPas, preferably of 10 dPas, and reliably accomplishes the filling process of the depressions 21.

The rollers 20.1 and 20.2 have a diameter of between 100 and 200 mm, and the depressions 21 have a radius of between 3.5 and 6 mm, when glass balls with a diameter of between 7 and 12 mm are produced. In order to prevent cracks from being formed in the beads 12, the rollers 20.1 and 20. 2 are heated-up to between 270 and 350 C by means of radiation heat.

A plurality of circumferential rows of depressions 21 may be disposed in the axial direction, which are alternately offset from one another by half a spacing and interleaved with one another in order to obtain intended breaking locations which are as short as possible between the beads 12. The intended breaking locations are fixed by the thickness of the glass strip 13 and determined by the dimension of the gap between the rollers 20.1 and 20.2. In consequence, the glass strip 13 between the beads 12 should not be too thick, and even the smallest value is critical in order to prevent cracks from being formed in the crude balls 14 during the subsequent breaking-off of the crude balls 14 from the glass strip 13. After the cooling and hardening of the glass strip 13, containing the beads 12, the

lotion process is effected by means of a separating device, e.g. a drum or tively a hammer device.

ude balls 14, thus obtained, are subjected to a cold surface finishing ant, for which purpose a coarse-grinding process, a fine-grinding process, ng process and/or a polishing process may be accomplished depending desired surface finish.

Claims

1. Method of producing glass balls, characterized in that a glass flow (11) is fed between two rollers (20.1; 20.2), which are driven synchronously but contrarotatingly in the flow direction, from a feed tank (10) containing a mass of molten glass, said rollers having hemispherical depressions (21) distributed over the circumference and forming spherical beads (12) on a thin glass strip (13) successively in the region of an imaginary contact tangent, in that the thickness of the glass strip (13) is fixed by the spacing between the rollers (20.1;

20.2) externally of the depressions (21) in the region of the contact tangent, in that crude balls (14) are separated from the glass strip (13) by means of a separating device once the glass strip (13), containing the spherical beads (12), has been cooled, and in that these crude balls (14) are subjected to a cold surface finishing treatment.

2. Method according to claim 1, characterized in that the glass strip (13) , between the spherical beads (12), is in the form of intended breaking locations having a thickness of about 1.5 mm

3. Method according to claim 1 or 2, characterized in that the rollers (20.1; 20.2) are heated-up to about 270 to 300 C by means of radiation heat.

4. Method according to one of claims 1 to 3, characterized in that the glass flow (11) is supplied to the rollers (20.1; 20.2) from the feed tank (10) with a temperature of between 1000 and 1200 C and a low viscosity of between 1 and 50 dPas, preferably about 10 dPas, at a throughflow rate of between 200 and 250 g/min.

Method according to one of claims 1 to 4, characterized in that the rollers 20.1; 20.2) having a diameter of between 100 and 250 mm are used, and depressions having a radius of between 3 and 10 mm are used.

Method according to one of claims 1 to 5, characterized in that rollers 20.1; 20.2) are used, wherein the depressions (21) are disposed in circumferential rows on the roller surfaces with uniform spacings erebetween, the adjacent circumferential rows being interleaved with !ach other so as to be offset from each other by half a spacing.

Apparatus for producing glass balls according to the method of the Invention, characterized in that a glass flow (11) can be supplied from a red tank (10), containing a mass of molten glass, to a shaping device aving two rollers (20.1; 20.2), which are driven synchronously and ontrarotatingly and have hemispherical depressions (21) to form a thin lass strip (13) having spherical beads (12), in that, once the glass strip 13) has cooled, the beads (12) are separable from the glass strip (13) as rude balls (14) by means of a separating device (15), and in that the ude balls (14) are then subjected to a cold surface finishing treatment.

ethod of producing glass balls substantially as hereinbefore described.

pparatus for producing glass balls substantially as hereinbefore Ascribed with reference to the accompanying drawing.

lass balls whenever produced in accordance with the method of at least aim 1.